The present invention relates to an X-ray optical system for converting an X-ray beam having a linear section into a converging beam focused on a point with the use of a polycapillary optics.
In the field of an X-ray diffraction apparatus, there is known a particular technique, which easily changes over between an optical system for the parallel beam method and another optical system for the Bragg-Brentano focusing method, the technique being disclosed in U.S. Pat. No. 6,807,251 B2, which will be referred to as the first publication hereinafter.
FIG. 13 is a perspective view illustrating an incident optical system of an X-ray diffraction apparatus disclosed in the first publication, in which an optics for the parallel beam method has been selected. An X-ray source 10 generates an X-ray beam 12 having a linear section. The X-ray beam 12 passes through the second aperture 16 of an aperture slit plate 14, and thereafter is reflected by a parabolic multilayer mirror 18 to become a parallel beam 20. The parallel beam 20 passes through an aperture 24 of an optical-path selection slit device 22, and thereafter passes through a Soller slit 26 and a divergence slit 28, and the parallel beam 20 is to travel toward a sample. What is incident on the sample is the parallel beam 20.
FIG. 14 is a perspective view illustrating another state of the incident optical system of the X-ray diffraction apparatus disclosed in the first publication, in which an optics for the Bragg-Brentano focusing method has been selected. As compared with the state shown in FIG. 13, the optical-path selection slit device 22 has been rotated by 180 degrees around its center, so that the position of the aperture 24 has been shifted to the right side. The X-ray beam 12 having the linear section passes through the first aperture 15 of the aperture slit plate 14, noting that the X-ray beam 12 is a diverging beam. The diverging beam passes through the aperture 24 of the optical-path selection slit device 22, and thereafter passes through the Soller slit 26 and the divergence slit 28, and the beam 12 is to travel toward the sample. What is incident on the sample is the diverging beam 12, which is usable as an incident beam in the X-ray diffraction apparatus using the Bragg-Brentano focusing method. The diverging beam has a divergence angle, which is regulated by a slit width of the divergence slit 28.
When using the incident optical system shown in FIGS. 13 and 14 in the X-ray diffraction apparatus, changeover is easily made between the parallel beam method and the Bragg-Brentano focusing method only by rotation of the optical-path selection slit device 22. In this case, the height H (vertical size in FIGS. 13 and 14) of the X-ray irradiation region on the sample is almost the same as the length L of the linear X-ray source 10.
Incidentally, the present invention is concerned with the conversion of the parallel beam into the converging beam with the use of the polycapillary optics. Such a conversion technique is disclosed in Japanese Patent Publication No. 7-40080 B (1995) (the second publication).
The second publication discloses that one end of the polycapillary optics is adapted to receive a parallel beam and the other end is adapted to discharge a converging beam, so that the converging X-ray beam is incident on a small region of a sample. The use of the polycapillary optics provides the converging beam with a higher X-ray intensity per unit area.
Besides, the present invention is also concerned with a combination of the polycapillary optics and the parabolic multilayer mirror. In connection therewith, a combination of a flat monochromator and the polycapillary optics is suggested in Japanese Patent Publication No. 2004-205305 A (the third publication).
The third publication discloses a total-reflection fluorescent X-ray analysis apparatus, in which an X-ray source generates an X-ray beam, which is then made monochromatic by a flat monochromator, and thereafter enters into one capillary tube of a total-reflection type. The capillary tube has an exit, which is narrowed in inner diameter so as to discharge a converging beam. The third publication also describes that a bundle of plural capillary tubes are usable instead of one capillary tube.
In the parallel beam method shown in FIG. 13, when it is planned to carry out X-ray diffraction measurement for a small region of a sample, it is necessary to reduce the sectional size of an X-ray beam arriving at the sample so that the X-ray beam is incident on the small region only. The first method therefor is to use a point X-ray source instead of the linear X-ray source. The second method is, as shown in FIG. 15, to arrange a selection slit device 32 for small region, which is formed with a small aperture 30, behind a multilayer mirror 18, and to add a height-restriction slit 34 at a divergence slit 28, i.e., the second method uses a two-slit optics for the small region. When the first method is adopted, it is necessary to prepare the point X-ray source other than the linear X-ray source, or to prepare a special X-ray tube whose focus can be changed over between the line focus and the point focus. When the second method is adopted, the major part of the parallel beam 20 is interrupted by the selection slit device 32 and the height-restriction slit 34, so that the intensity of the X-ray beam 21 arriving at the sample is remarkably reduced.
Incidentally, when the prior art disclosed in the second publication is used, it is sure that a converging beam focused on a point is obtained from the parallel beam, but the obtained beam is not monochromatic. In addition, the parallel beam that should be received is considered to be a parallel beam with a circular section, that is to say, the second publication does not mention the conversion of the X-ray beam having the linear section into a converging beam focused on a point. Further, the second publication does not mention changeover from an optics providing a converging beam focused on a point into another optics.
When the prior art disclosed in the third publication is used, there is obtained a monochromatic beam because the flat monochromator is used, and the obtained beam converges on a point. However, the parallel beam that should be received is considered to be a parallel beam with a circular section, that is to say, the third publication does not mention the conversion of the X-ray beam having the linear section into a converging beam focused on a point. Further, the third publication does not mention changeover from an optics providing a converging beam focused on a point into another optics.